This invention relates to improvements in capillary or open tubular columns that are used in gas chromatography to cause the constituents of sample material introduced at one end to emerge from the other end at different times.
Glass capillary chromatography columns, as they are used in the present state of the art, are formed by drawing a large diameter glass tube to form a straight stiff glass tube of the desired dimension, being typically 0.25 mm. inside diameter and 0.8 mm. outside diameter. The process is described in an article entitled "Construction of Long Lengths of Coiled Glass Capillary" at page 302 of the 1960 issue of Analytical Chemistry. After the glass column is drawn and has cooled, it is forced through a heated coiling tube which operates at a temperature above the annealing point of the glass and which serves to form the drawn tube into a coil being typically 10 to 15 centimeters in diameter, the tube being from 10 to 100 meters in length. The inside surface of these tubes is first etched with acid and then deactivated with a thin layer of suitable material so as to make it more inert for the particular sample material involved. This deactivating coating is then coated with a thin layer of stationary phase to form a column.
Glass capillary chromatography columns have several disadvantages in use, namely, that they are fragile and are easily broken if overstressed. Because they are relatively inflexible, the ends of the column must be straightened by heating them to the softening point in order to attach them to the injection port and detector fittings of a conventional gas chromatograph. Alternatively, transfer lines must be constructed to which the column can be connected and which are then connected to the injection port and detector fittings in the gas chromatograph.
A greater disadvantage of glass columns is that they distort peak shapes of sample materials that are as acidic as substituted phenols or as basic as aliphatic amines or otherwise reactive such as mercaptans, even if the surface is deactivated with organochlorosilicanes or with oxygenated polymers, such as poly(ethylene oxide) or polysiloxanes. This effect is caused by chemical activity of the glass surface, causing sample materials which are strongly acidic or basic or otherwise chemically reactive to adsorb strongly to the glass surface, causing these sample components not to elute from the column, or to elute with peak shapes seriously distorted from the usual symmetrical shape.
In an article entitled "The Origination, Development and Potentialities of Glass Capillary Columns" at page 452 of the September 1975 issue of Chromatographia, Vol. 8, No. 9, the possibility of silica capillaries is mentioned, but if columns of silica were made in the same way as glass columns, considerable difficulty would be encountered because the softening temperature of silica is much higher than the melting temperature of materials from which the coil forms are generally made. Furthermore, even if a column were made in this manner, softening the ends of the column so that they can be straightened as required to slide into the fittings of the instrument would require special heating means capable of producing high temperatures.
Furthermore, it has been reported that silica is not a suitable support for the stationary phase because silica catalyzes the breakdown of the macromolecules of the stationary phase and causes it to change slowly from a liquid to a quasisolid state. This is noted in an article entitled "The BaCO.sub.3 Procedure for Preparation of Glass Capillary Columns: Further Information and Development" at page 181 of the publication Chromatographia, Vol. 10, No. 4, of April 1977.